The authors arrive to a conclusion that is totally in contradiction with a paper published in Geophysical Prospecting, Vol. 21, No. 4 (Dec. 1973), 626-634, by A. Roy and Shikhar C. Jain. It can be argued that one (Beard-Tripp) is based on speculative data, while the other (Roy-Jain) is experimental, but the differences are not acceptable. IP users need to clarify this situation.